1. Field of the Invention
This invention relates to a secondary battery using lithium as an active material, and further to an improvement of a negative electrode.
2. Description of the Prior Art
Currently, materials for use as a negative electrode in a secondary battery using lithium, which may be comprised of carbon compounds, including coke and the like, are tested for lithium metal content. The metals are tested because the carbon compounds have superior reversibility on charge-discharge cycles and substantially prevent electrical deposition from a mossy lithium on a surface of the negative electrode.
However, carbon compounds of coke or the like are not always a suitable material for the negative electrode. A long cycle life or a decrease of charging frequency do not always produce a sufficient discharge capacity. For example, ordinary materials such as coke have a electrical capacity of about 240 mAh/g. When using coke for the negative electrode to obtain an AA size secondary battery, the maximum capacity of the battery is about 350 mAh, or at most 400 mAh.
Research reported by YAMAGUCHI UNIV. and SENTRAL GLASS Co. discusses carbon compounds having the formula BC.sub.2 N. However, these carbon compounds includes comparatively high levels of nitrogen (N), and the conductivity of these carbon compounds is low. Therefore, carbon compounds need to be improved to be used as negative electrode materials.